Lower body negative pressure protects brain perfusion in aviation gravitational stress induced by push-pull manoeuvre

The acute negative (-Gz) to positive (+Gz) gravity stress during high-performance aircraft push-pull manoeuvres dramatically reduces transient cerebral perfusion, which may lead to loss of vision or even consciousness. The aim of this study was to explore a specific and effective counteractive strategy. Twenty-three healthy young male volunteers (age 21 1 year) were subjected to tilting-simulated push-pull manoeuvres. Lower body negative pressure (LBNP) of -40 mmHg was applied prior to and during -Gz stress (-0.50 or -0.87 Gz) and released at the subsequent transition to +1.00 Gz stress. Beat-to-beat cerebral and systemic haemodynamics were continuously recorded during the simulated push-pull manoeuvre in LBNP bouts and corresponding control bouts. During the rapid gravitational transition from -Gz to +Gz, the mean cerebral blood flow velocity decreased significantly in control bouts, while it increased in LBNP bouts (control vs. LBNP bouts, -6.6 4.6 vs. 5.1 6.8 cm s(-1) for -0.50 Gz, and -7.4 4.8 vs. 3.4 4.6 cm s(-1) for -0.87 Gz, P < 0.01), which was attributed mainly to the elevation of diastolic flow. The LBNP bouts showed much smaller reduction of mean arterial blood pressure at the brain level than control bouts (control bouts vs. LBNP bouts, -38 +/- 12 vs. -23 +/- 10 mmHg for -0.50 to +1.00 Gz, and -62 +/- 16 vs. -43 +/- 11 mmHg for -0.87 to +1.00 Gz, P < 0.01). LBNP applied at -Gz and released at subsequent +Gz had biphasic counteractive effects against the gravitational responses to the push-pull manoeuvre. These data demonstrate that this LBNP strategy could effectively protect cerebral perfusion with dominant improvement of diastolic flow during push-pull manoeuvres.